The NIH Roadmap and NCI strategic plans repeatedly invoke the need for greater involvement of healthcare systems in research. Integrated delivery systems, which provide comprehensive care from prevention to palliation, can address key research questions about cancer prevention and control that cannot be answered in many other settings. A consortium of healthcare systems with internal research capabilities creates an unprecedented opportunity to study variations in policy and patterns of cancer prevention and care. In recognition of this potential, the National Cancer Institute issued a Request for Applications in 1997 to "facilitate the conduct of NCI sponsored research on cancer prevention...detection... [and] treatment" through collaboration among health care delivery systems. In response a group of HMOs (10 collaborators initially, and 13 in the proposed application), formed the HMO Cancer Research Network (CRN), whose overall objective is to conduct research that improves the effectiveness of cancer prevention and treatment through research that identifies individual, provider, system and treatment factors that affect outcomes. We propose herein a research infrastructure and array of projects that capitalize on the unique facets and contributions of a network of delivery systems. The proposed Cancer Research Network consists of four cores, five projects, and a research emphasis on translation of cancer care innovations in community settings. The CRN infrastructure supports our overall goals through a rich, interconnected set of shared resources, and collectively, the projects exploit the CRN's geographic diversity and its sophisticated automated data capabilities. CRN projects are designed to pinpoint the ways in which community-based health care systems can best respond to their enrolled members by: 1) ensuring that they receive the right cancer prevention services;2) devising cancer prevention messages that are readily understood and used;3) providing treatment that is both effective and cost effective to those patients with cancer;and 4) responding holistically to patients'physical and psychosocial needs. Research in the CRN will be readily applicable across health care settings and will contribute to overall improvements in the quality of cancer care.